Both the US Embassy and the Pentagon said they couldn't give specifics on the nature of the American support for "security reasons."

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The Pentagon noted that US Special Operations Forces "have been providing support and assistance in the southern Philippines for many years, at the request of several different Filipino administrations."

The number of troops there ranges between 50 to 100 at any given time, the Pentagon said.

"As we have in the past, we routinely consult with our Filipino partners at senior levels to support the Duterte administration's counterterrorism efforts," the embassy said, referring to President Rodrigo Duterte.

A 'temporary setback'

At least 13 Philippine marines were killed and 40 others wounded Friday during fighting with Maute militants in Marawi, the Philippine military said Saturday.

The fatalities occurred during a clearing operation over a 14-hour period.

"Save Marawi City" T-shirts are sold in Manila to help victims of the fighting.

The deaths bring the toll in the three-week Marawi campaign to 58 Philippine troops and at least 140 extremist militants, according to the state-run Philippine News Agency.

"This temporary setback has not diminished our resolve a bit," said Marine Col. Edgard Arevalo, a military spokesman.

"It instead primed up our determination to continue our prudent advances to neutralize the enemy, save the innocent lives trapped in the fight, and set the conditions for the rehabilitation and reconstruction of Marawi."

Fighting the militants' message online

The fight against the Maute militants is proceeding on social media as well as the ground.

The Philippine military has called on Facebook to close 63 accounts linked to Maute militants engaged in the fighting.

At a press conference Friday in Marawi, Lt. Col. Jo-Ar Herrera said the military had uncovered accounts used by militants that focus on "spreading propaganda messaging and misinformation."

It explored the root cause of such extremism and offered suggestions on how to confront radicalization.

The government said it is preparing infrastructure repairs in Marawi once the region is cleared.

"We assure you that the President is deeply concerned for the city, the region and the island's well-being and is very hands-on to ensure that normalcy will be restored at the soonest possible time and serve people's aspirations for a comfortable life for all," presidential spokesman Ernesto Abella said, speaking on a radio program.